This invention relates to circuitry for providing an interface between a host computer and multiple peripheral devices. More particularly, the invention relates to means for interfacing multiple electronic devices such as modems, pagers, faxes, or other circuitry to a computer via a single PCMCIA slot.
Communication devices such as pagers and electronic mail receivers, which allow people to be contacted even when away from a telephone, are becoming increasingly popular. Callers can send short numeric or alphanumeric messages to a service subscriber. A typical numeric paging message is the telephone number of the caller. Wireless electronic mail ("e-mail") receivers allow the user to receive longer alphanumeric messages, as well as information provided by various subscription services.
Due to their small size and limited power source (i.e. a battery), pager and e-mail receiver displays are less than ideal. It would therefore be desirable if messages could be downloaded from an e-mail receiver or pager to a personal computer (PC) or other host device. Because of their relatively small size and weight, a laptop or palmtop computer would be an ideal host device for a pager or e-mail receiver. Presently, many of these small computers come equipped with one or two PCMCIA (Personal Computer Memory Card International Association) expansion slots. Named after the Personal Computer Memory Card International Association, of Sunnyvale California, the PCMCIA specification was originally drafted to cover so-called memory cards; however, numerous devices conforming to PCMCIA specification are now available, including, for example, serial ports, hard disk drives, network interfaces, and Global Positioning System (GPS) receivers.
As is well-known, computers can communicate over telephone lines using modems, and many PCMCIA modems are available. In order to add wireless e-mail (or paging) and modem capabilities to a computer system, it has generally been necessary to add both e-mail and modem units. Because this requires the use of two separate devices, two computer slots or communication ports must be used. In a laptop computer, which may have only one or two PCMCIA expansion slots, using two devices may not be possible, or at best would use up all available slots and leave no room for further expansion or upgrade. Although, the PCMCIA standard allows for hot-swapping of devices, this is not a very desirable or practical method of using multiple PCMCIA devices when there are more devices than available slots.
One possible solution to this problem would be to combine the pager or wireless e-mail receiver with a modem into a single integrated PCMCIA card. Such a device, combining a fax/data modem and a radio pager is disclosed in co-pending commonly assigned U.S. patent application Ser. No. 08/174,797, which is incorporated herein by reference. With such a device a user would only need one PCMCIA slot to use both modem and pager communication devices. This approach is not without its drawbacks, however. Due to the specified dimensions of a PCMCIA slot and card, and due to the need to provide the pager with a battery for power when it is not connected to the computer, the combined pager/modem device has bulkier packaging than either the pager or PCMCIA modem alone. It would therefore be advantageous to be able to separate the modem (PCMCIA card) and e-mail receiver or pager components of the device from each other.
Another drawback to the combination approach is that a user is limited to those particular combinations of peripherals being offered by the various manufacturers. The computer user, therefore, does not have flexibility in choosing the combination of peripherals. Furthermore, the user may prefer that certain peripherals are built by specific, and possibly different, manufacturers. Indeed, for special purpose peripherals there may be only one vendor available. Such circumstances may preclude purchasing a single integrated device having all the desired component functionality. It would therefore be desirable to provide a low cost and easily implemented interface between the host computer and the peripheral that would permit the user to "mix-and-match" component devices from various manufacturers.
An alternative to the integrated device approach would be to develop and standardize a means for multiple devices to share a single PCMCIA interface. The PCMCIA specification provides for a 15 pin peripheral connector, or auxiliary port, which is intended to allow a PCMCIA card to connect to the external world. The auxiliary port has been used to connect a PCMCIA device to, for example, a network, a telephone line, or an external floppy diskette drive. Often such connections utilize a subset of the 15 pins available in the auxiliary port connector. It would therefore be desirable to include additional circuitry on a PCMCIA device to make it possible to configure some of the unused pins as a serial bus for connecting additional devices to the host computer.